1. Field of the Invention
The present invention relates generally to a submerged nozzle change device or a change device for submerged nozzles. More specifically, the invention relates to a change device for a submerged nozzle used for allowing a molten metal to run out of a molten-metal containing vessel.
2. Description of the Prior Art
An example of a conventional submerged nozzle change device is shown in FIG. 13A. As shown in a vertical section of FIG. 13A, an insert nozzle 2 is inserted into a molten-metal outlet formed in the bottom of a molten-metal containing vessel 1, such as a tundish or a ladle. A slide valve unit 3 is arranged directly below the insert nozzle 2. The slide valve unit 3 has an upper plate 4 having a through hole 4a. The lower portion of the insert nozzle 2 is formed on the upper plate 4 of the slide valve unit 3 around the through hole 4a. A submerged nozzle 5 is arranged directly below the slide value unit 3. The periphery of the upper portion of the submerged nozzle 5 is covered with a metal case 6, so that the submerged nozzle 5 is suspended from and supported on a submerged-nozzle supporting unit 7 via the metal case 6.
As shown in FIG. 18, in the case of a continuous casting apparatus, the lower portion of the submerged nozzle 5 is submerged in a mold 8 having a water-cooled structure, so that a molten metal 9 flows continuously into the mold 8 through an outlet 5a formed in the periphery of the lower portion of the submerged nozzle 5. The peripheral surface of the molten metal 9 is cooled in the mold 8, so that the molten metal 9 is solidified therein. Then, the solidified molten metal 9 is drawn out from the lower portion of the mold 8 to be led to the next process.
As shown in FIG. 13A, the slide valve unit 3 also has a slide plate 10 having a through hole 10a. The slide plate 10 is connected to a piston rod of a hydraulic cylinder (not shown in FIG. 13A) to slide in horizontal directions (in directions perpendicular to the plane of FIG. 13A) by means of the hydraulic cylinder. In addition, the slide valve unit 3 has a lower plate 11 having a through hole 11a. When the slide plate 10 slides in horizontal directions by means of the hydraulic cylinder, the hole 10a of the slide plate 10 is brought into and out of register with the hole 4a of the upper plate 4 and the hole 11a of the lower plate 11 to establish and block a fluid communication so as to control the outflow of the molten metal.
The upper end portion of the submerged nozzle 5 is formed as an enlarged-diameter portion which is covered with the case 6 of a metal. The upper-end contact surface of the submerged nozzle 5 is brought into tight contact with the lower surface of the lower plate 11. Since the lower plate 11 may be a lower nozzle, the lower plate 11 will be referred to hereinafter as a lower nozzle 11.
As mentioned above, the lower portion of the submerged nozzle 5 is always submerged in the molten metal in the mold 8. Therefore, wear and damage of the lower portion of the submerged nozzle 5 may be caused by the molten metal, so that it is required to timely change the submerged nozzle 5 to a new submerged nozzle 51.
Therefore, as shown in FIGS. 13A, 13B and 14, the conventional submerged nozzle change device is provided with a pair of rails 12, which are provided on both sides of the submerged-nozzle supporting unit 7 arranged below the slide valve unit 3 and which can slidably support the submerged nozzle 5 thereon. After the new submerged nozzle 51 is set between the pair of rails 12, the new submerged nozzle 51 is pushed as shown in FIG. 15 by means of a piston rod 13a of a hydraulic or pneumatics pressing cylinder 13 supported on the lower surface of the molten-metal vessel 1, whereupon a spent submerged nozzle (which will be hereinafter referred to as an old submerged nozzle 52) is moved to the opposite side of the rails 12, from where the old submerged nozzle 52 is removed.
Furthermore, as can be seen from FIGS. 13A and 14, the submerged-nozzle supporting unit 7 has two sets of supporting members 14 on the right and left sides. Each set of supporting members 14 are oscillatably supported on the lower surface of the slide valve unit 3 at the intermediate portions thereof via a shaft 15. A plurality of springs 16 are provided between the upper surfaces of the outer end portions of the respective supporting members 14 and the lower surface of the slide valve unit 3, so that the inner end portions of the respective supporting members 14 are biased upwards. Thus, the upper-end contact surface of the submerged nozzle 5 suspended between the supporting members 14 is brought into tight contact with the lower surface of the lower nozzle 11 to be fixed thereto.
According to the above described conventional submerged nozzle change device, the time required to change the submerged nozzle 5 may be short, and the time to stop the outflow of the molten metal may be short in the case of the continuous casting. Therefore, there are advantages in that the scrapping of the molten metal can be reduced and the yield thereof can be improved.
However, in the conventional submerged nozzle change device, when the submerged nozzle 5 is changed, the upper-end contact surface of the new submerged nozzle 51 is caused to slide on the lower surface of the lower nozzle 11 to a predetermined position while a surface pressure is being applied to the upper-end contact surface of the new submerged nozzle. In addition, a seal member, such as a packing, can not be used. Therefore, the upper-end contact surface of the new submerged nozzle 51 may easily be scratched to produce gaps between the upper-end contact surface of the new submerged nozzle 51 and the lower surface of the lower nozzle 11 so that air is allowed to enter through the gaps and the molten metal is oxidized.
In particular, if a metal 17 is adhered to the inner periphery of the old submerged nozzle 52 and solidified as shown in FIG. 16, the metal 17 is difficult to be cut even if the new submerged nozzle 51 is pushed by the piston rod 13a of the cylinder 13 to move out the old submerged nozzle 52. Even if the metal 17 is cut, the cut metal 17 projects from the lower nozzle 11 as shown in FIG. 17. In this state, if the new submerged nozzle 51 is caused to slide on the lower nozzle 11, the upper-end contact surface of the new submerged nozzle 51 will be scratched and impair the degree of tight contact of the new submerged nozzle 51 with the lower nozzle 11.